A major site for productive HIV infection is the lymph node. HIV replication is robust in this tissue compartment despite the presence of lymphocytes such as natural killer (NK) cells that can potentially control HIV infection. Even more intriguing is the fact that robust viral replication takes place under circumstances that promote NK cell killing activity such as 1) the presence of elevated levels of cytokines (i.e., IL-2, -12 and -15) which enhance NK cell mediated cytotoxicity and promote the development of effector NK cells from na[unreadable]ve NK cells, 2) the decreased expression by infected cells of molecules [e.g., major histocompatibility molecules (MHC) class I molecules] that provide inhibitory signals to NK cells (i.e., HLA-A and -B) and, 3) the expression by infected cells of surface molecules that provide activating signals to NK cells (i.e., ULBPs). Our objective is to determine why HIV prevails in lymph nodes despite an environment that favors NK cell mediated killing of HIV infected cells. Our hypothesis is that HIV evades NK cells in the lymph node through 1) its ability to alter the makeup of the NK cell population in the lymph node so it consists mostly of unresponsive NK cells (i.e., CD56negCD16pos), and 2) its ability to decrease the expression of molecules on infected T-cells that trigger NK cell responses (i.e., CD48 and NTB-A) while maintaining the expression of inhibitory molecules (i.e., HLA-C). To test this hypothesis, inguinal lymph nodes will be obtained from HIV-infected and uninfected subjects, lymphoid NK cells will be isolated and the capacity of NK cells in the lymph node of HIV-infected individuals to destroy HIV infected cells will be determined. This will initially be accomplished by determining the overall cytotoxic capability of lymphoid NK cells to kill autologous peripheral blood CD4pos T-cells infected with a primary strain HIV-1SF162. The cytotoxic activity of NK cells will be compared with the levels of cytokines produced by cells in the lymph nodes. The distribution of the different lymphoid NK cell subsets will also be determined by multicolor flow cytometry. Moreover we will determine the various inhibitory and activating receptors on NK cells by multicolor flow cytometry. In addition, HIV-infected T-cells will be obtained from lymph nodes and the susceptibility of these cells to autologous lymphoid NK cells will be determined. The final step will be to characterize the expression on HIV-infected cell's surface of various ligands that bind to receptors that provide positive and negative signals to NK cells. Our expectation is that in the lymph node of HIV-infected individuals, NK cells will have impaired cytotoxicity and that infected lymphoid T-cells will be resistant to NK cells because of the simultaneous retention of inhibitory molecules and the decreased expression of activating molecules on the infected cell surface. The findings from this study will provide insights into the mechanisms by which HIV evades NK cells in lymph nodes. These insights, in turn, will provide the rationale for investigating new treatment strategies that can enhance the immune control of HIV. PUBLIC HEALTH RELEVANCE: This project will determine how HIV evades immune cells called natural killer cells in the lymph nodes, which is a major site for productive HIV infection. The results from this study will provide insights on the mechanisms by which HIV avoids detection and destruction by the immune system. These insights will point the way towards treatment strategies that will enhance the immune system's ability to control HIV.